Apparatus for drawing fibers



May a, wu.: N. s. KAPANY Erm.

APPARATUS Foa DRAWING FIBERS Filed June 1. 1960 5 Sheets-Sheet 1 IN VEN TORSI NARlNDER S. KAPANY DAV\B F. CAPELLARQ May 7, 1963 y N. s. KAPANY ETA; C 3,088,297

APPARATUS FOR DRAWING FIBERS I Filed June 1, 1960 5 Sheets-Sheet 2 ...Fi-* Q 2 l may COMPENSATING 2\ slcaNAL 35e, 34 SERV seRvo lseLEcToR P/ AMP. MOTOR j l 4Z RATE $\GNAL COMPENSATNG SIGNAL DIAMETER 50 SELECTION UNIT sanvc simo mu?Y Mo-ron )3 la 39 RATE sieNAL 4 /7 ,6 DITJ'QFTE AN COMPENSATED CONTROL 5/ ,49 4/ SlGNAL ksemo M01-cn ll y 5m' ma 44 l6o 52 l 45) f1 INVENroRs: NARmDER s. KAPANY DAym F. CAPELLI-mo May 7', 1963 N. s. KAPANY ErAL 3,038,297

v AIPARATUS FOR DRAWING FIBERS i Filed June 1. 1969 5 Sheets-Sheet 3 INVENTORSI NAR\NDER 5. KAPANY BQAVHD F. CAPELLARQ May 7, 1963 Filed Junevl, 1960 N. s. KAPANY r-:rAL 3,088,297

APPARATUS FOR DRAWING FIBERS 5 Sheetsf-Sheet 4 OVERALL.

SPEED CONTROL WMM May 7, 1963 N. s. KAPANY Erm. 3,088,297

APPARATUS Foa DRAWING FIBERs 5 Sheets-Sheet 5 Filed June 1, 1960 INVENTORS: NARINDER S. KAPANY DBV|D F CAP ELLARO United States Patent O 3,088,297 APPARATUS FOR DRAWING FIBERS Narinder S. Kapany, Chicago, and David F. Capellaro, Glen Ellyn, Ill., assignors, by mesne assignments, to American Optical Company, a voluntary association of Massachusetts Filed June l, 1960, Ser. No. 33,240 4 Claims. (Cl. 65-13) The present invention is directed to fiber drawing apparatus and more particularly, such apparatus whereby fiber size is maintained constant within small tolerance by varying one of several parameters which affect such size.-

A number of factors influence the diameter of drawn fibers, Principal among these are the chemical composition of the material in the furnace, the temperature of the furnace affecting the viscosity of the material and the rate at' which the fiber is drawn from the furnace.

Up to the present time many machines have been designed whereby drawn fibers would have uniform diameters. Such machines generally embody two principles. First; the drawn fibers may be made to contain uniform diameters by regulating the fiber drawing rate. For eX- ample, if the fibers were reeled on a drum, the angular velocity of such drum must decrease in predetermined steps to account for the increasing radius caused by the wound fibers. That is to say, the take-up drum would decrease its revolutions per minute by discrete percentages at definite time intervals. This method exhibits an inherent difliculty in that temperature variations in the furnace or imperfections in the fiber material may cause variation in fiber diameter notwithstanding constant fiber drawing rates. Second; the temperature of the furnace melting the liber material (hereinafter referred to as glass rod) may be varied, thereby varying the viscosity of such material and consequently, changing the ber diameter for a given winding rate. Exemplary difficulties with this technique are: (l) the time delay required in changing the furnace temperature, necessarily adding to the cost of the process; and (2) the fiber drawing rate can cause nonuniformity in fiber diameters independent of furnace temperature changes.

At ths point, one might say a combination of the two above described techniques should obviate the diiculties mentioned. Perhaps it would; however, this combination would be cumbersome and would require almost constant supervision by a machine operator. Further, it is believed that the time delay caused by furnace temperature change would not be completely eliminated. Still further, a method of detecting changes in liber diameter must be employed before corrective action may be taken.

It is accordingly, a general object of the instant invention to provide a novel fiber drawing means which obviate the disadvantages incident to those available in the past.

Another object is to devise means which will draw uniform flexible bers within the accuracy necessary to eni able such fibers to beused as optical components.

A different object is to devise drawing means for producing optical fibers whereby once such means is set into operation the machine will produce such fibers autonomously.

A more specific object is to devise a fiber drawing machine whereby substantially uniform optical fibers are produced by continuously monitoring the fiber diameter.

Another different object is to produce coated optical fibers of substantiallyuniform diameter by continuously monitoring the fiber diameter and comparing any changes thereof to a preset standard and controlling the apparatus therewith.

Still another object is to devise a fiber drawing machine whereby fused, aligned, substantially uniform optical fiber lCC 'more apparent from the specification and the drawings wherein:

FIGURE l is a perspective view, partly in section, of most of the essential elements of the instant invention.

FIGURE 2 is a block diagram of a fiber drawing ma-y chine embodying the principles of the instant invention. FIGURE 3 is a schematic perspective view partly in section of a furnace which may be used in the instant invention.

FIGURE 4 is an enlarged perspective view of a means for coating the drawn fibers in accordance `with the principles of the instant invention.

FIGURE 5 is a schematic representation of one type of fiber measuring means.

FIGURE 5A is an enlarged view of the triangular aperture 31.

FIGURE 6 is a diagram useful for explaining the operation of measuring means of FIGURE FIGURE 7 is a schematic diagram of an electromechanical tiber diameter measuring unit.

FIGURE 8 is a schematic perspective view of the takeup drum and the traverse unit. v u

FIGURE 9 is a block diagram of the preferred embodiment of the disclosed invention. i

FIGURE 10 is a perspective illustration partly in section of the take-up and traverse means employed in the preferred embodiment.

FIGURE l1 is a top view of part of the meansv shown in FIGURE 10 illustrating an arrangementof the takeup motor and the supports for take-up drums 49.

FIGURE l2 depicts a furnace which may be employed in conjunction with, or in place of, furnace 13.

FIGURE 13 is a view of asection of the furnace shown in FIGURE 12. l

Before describing our apparatus in detail, it will be helpful to outline the utility of superfine dielectricfibers as optical components. It is well known that one or a bundle of flexible dielectric fibers will transmit radiant energy from one end to the other. Hence, optical images (a form of radiant energy) impinging one end of an aligned bundle of fibers are reproducible at its opposite end. Of course, an individual fiber or a multitude thereof may act as a light transmitter. This light transmission depends on the principal of total internal reflection from the side walls of the conducting element of the light which has entered at one end of the element, thereby allowing this light to be transmitted therethrough to the opposite end thereof. It has been found that improvements occur when the individual fibers are individually coated with a thin layer of a material having a lower refractive index than that of the fiber itself. Also, an additional coating of an opaque material is desirable in certain cases. Furthermore, the resolving power of-such a transmission means is primarily dependent upon fiber diameter and has been found to improve with lesser ber diameters. It follows, therefore, that if the fiber bundle consisted of aY multitude of uniformly small diameter fibers it would have high resolving power.

For a more detailed analysis of the utility of dielectric fibers the readers attention is directed to co-pending application Serial Number 750,811 filed July 24, 1958,'now abandoned and assigned to the assignee of the present invention. f

It is known that a length of thermoplastic dielectric 'rod 40 comprising a length of solid round dielectric encased within a hollow dielectric cylinder having a lower indet of refraction and concentric therewith, may be co-drawit such that the end product, fiber 40a, will bear substantially the same dimensional ratio in cross-section of rod and cylinder, as the glass material had in its original form. Use is made of this procedure to eliminate a multi-step drawing process. Hence, by this method the additional coating, if desired, is all that is necessary in the drawing process. Along these lines, it is noted that in the detailed description to follow, the glass rod 40 represents a solid rod of radiation transmittent material and a hollow cylinder encasing said rod, but having a lower refractive index and substantially the same melting point as that of the solid rod.

The fibers, rod or cylinders of the instant invention may be made of any dielectric material-viz., capable of transmitting electromagnetic radiation in the region of interest which may be ultra-violet, visible, infra-red or the microwave region. When used as a visible light transmitter, glass has been found to be an excellent material to meet the above-mentioned requirements and can he drawn into extremely small, flexible fibers. However, various plastic materials such as Lucite may also be used and many other similar transmissive materials will occur to those skilled in this particular art.

Turning to the drawings in detail, FIGURES l and 2 depict a fiber drawing machine for producing coated optical fibers, having an accurate speed glass rod feed means 11, which includes a velocity controlled servomotor that is regulated by amplifier 12. Amplifier 12 is responsive to control signals from master comparator 44 which establishes a predetermined rate of glass rod feed $0 to the four sectioned furnace 13. The mass of glass rod 40 fed into furnace 13 is immediately controlled by the feed means Il. A signal proportional to the rate of rod feed is continuously compared to a master control signal generated by master comparator 44 and transmitted to amplifier 12. Any error measured by amplifier 12 between the master signal and the rate signal from rod feed means 11 causes a compensating signal to be fed into rod feed means 11 causing the rod feed rate to change in a manner that reduces the measured error to zero.

FIGURE 3 is an enlarged perspective view of the four section tubular furnace 13. Furnace 13 is secured to, and supported by, frame 50 and is suspended such that the longitudinal axis thereof is concentric with the axis of the rod 40 fed thereto. The four tubular sections are controllable by means of pyrometers 35 through selection unit 34. In this way, known thermal gradients are established along the axis of the glass rod 40, to create optimum conditions for the fusion and production of bers 40a. Before the machine is set into operation the temperature of the individual sections of the furnace 13 are predetermined and set by means of pyrometers 35. Each section 13a-d has its own thermocouple at the heated surface and its ownl power supply leads. The power supplied to the furnace section 13a-d is contfolled by selection unit 34, which is controlled by pyrometers 35. As only two pyrometers are used to control the four furnace elements 13a-d, switches are provided in selection unit 34 in order that any combination of pyrometers 35 and sections 13a-d may be used in that a pyrometer may only be controlled from a thermocouple in a furnace element connected to it. A feature of these combinations is that in addition to the break protection afforded to the thermocouples, an indication if an incorrect thermocouple has been selected to control one of the pyrometers 35 is also available.

Assuming that the proper temperatures have been selected and the pyrometers 3S are connected in proper order; the temperature gradient established along the vertical axis of the furnace 13 is continuously checked by pyrometers 35a and 3511. Control signals from the pyrometers are supplied to selection unit 34 in order that said gradient be maintained constant throughout the drawing operation.

The selection of furnace temperature is dependent upon the rod material, and the fiber size required. The peak temperature within the furnace 13 usually varies from 800 to 1700" F. and generally this maximum tempera` ture is maintained approximately between elements 13e and 13d. It is understood, however, that any thermal gradient may be maintained. Furthermore, a greater or lesser number of furnace sections may be employed, the number of sections being controlled by the particular application called for.

There is a limitation on furnace temperature, however. Said temperature must be maintained below the point at which the solid dielectric rod and its surrounding cylinder would diffuse. On the other hand, the material is suficiently heated to enable its being drawn into a fine fiber. At the present time no tables exist tabulating the diffusion temperature between various dielectrics. However, such temperatures are experimentally determinable without much diiculty.

The cold rod 40 enters furnace 13 and by the time it reaches the region of section 13C and 13d a drop of glass is formed and eventually falls from the end of the rod drawing a fiber 40a with it. This drop is removed allowing a fiber to be wound onto the take-up drum 49.

If fiber 40a is required to be metallized, it is passed through a unit 14 which comprises a boat containing a molten globule 14e of the metal required for the coating. The coating material 14e need not be a metal; however, for optimum results, it should be opaque. To this end, we have coated with opaque glass, combinations of opaque and clear glass, lead, aluminum and indium. Of course, in all cases the coating material must be one that is fusible to the film 40a.

Referring .to FIGURE 4, the boat 14 is insulatingly supported from the frame 50 by elements 14a and 14b. Elements 14a and 14h in addition to acting as supports, supply electric power to the boat 14 as a heating element and thereby maintain the coating material 14c in its molten state. Fiber 40a passes into one side of boat 14 through molten material 14e` and out through a narrow V-shaped slit 15. Slit 1S is large enough to pass the fiber 40a, but small enough to prevent escape of the molten material 14C due to its surface tension. The molten coating material 14C is shown passing into the boat 14. The coating material supply reel and its operative association to servo-motor 16 have been omitted for illustration purposes only. Coating rod 14d may be wound on a supply reel which is belt driven by servomotor 16. And in a manner described below a constant supply of molten coating material is maintained while the machine is in operation.

Most metals which will serve as coating meda sufl'cr severe oxidation, which eventually produces a wcak and ineffective coating. Accordingly, where the coating material 14e` is liable to oxidation in its molten state, the present machine should bc enclosed in a cabinet containing an inert atmosphere. To this end, everything but the electric controls are mounted within the airtight framework 50 and said controls are mounted on a separate cabinet. The cabinet 50 is made airtight in a conventional manner and an inert atmosphere may bc circulated therethrough. The gas and pump means have been omitted from the drawings for purposes of clearness of illustration inasmuch as such mea'ns form no part of the instant invention and their application thereto would amount to the ordinary skill of an artisan.

A continuous coating feed means 16 including a velocity controlled servo-motor is provided to replenish molten material 14e as it is consumed. The rate of said feed means 16 is accurately regulated by amplitier 17 which is responsive to a master control signal from comparator 44. The coating feed rate is regulated in the same manner as rod 40 feed rate. That is to say, any error between the master control signal and the rate signal causes a compensating signal to be generated which changes the coating feed rate in a direction to reduce said error to zero.

The heart of the system is ber diameter measurement means 18 in that the rates of the: glass rod feed 11; coating rod feed 16; take-up drum 51; and traverse unit 52 are all governed by said measurement means 18.

Fiber diameter measurement means 18 generates a signal proportional to ber diameter and such signal is fed into differential amplifier 41 and compared with a signal from control 42 corresponding to the desired fiber diameter size. Control 42 may take many forms and this case comprises a calibrated potentiometer whereby signal magnitude is correlated to liber diameter. In this manmr, a preset amplitude which will correspond to a selected ber diameter will control the various rates of the dierent mechanisms which comprise the ber drawing machine. Any error measured, is fed into master comparator 44. Inorder to determine the degree of error, the desired diameter signal is compared .to the error signal. This is effected by coupling the signal from desired ber diameter signal means to comparator 44. Master comparator 44 is a composite of four signal generators responsive to an input error signal de# rived from the fiber diameter measuring means. However, such generators each transmit a master control signal, by means of connections 45-48 inclusive, to their respective circuits in such magnitudes that the control signals, if any, all bear a ratio in magnitude with ,respect to each other. In other words, the rate change of glass rod feed means 11 will be a submultiple of the rate change of take-up of drum means 51 because the mass of glass rod 40 fed into furnace 13 should always equal the mass of fiber 40a drawn for any given ber diameter. For example, if a rod diameter attenuation of one thousand were sought, the linear drawing rate must be one million times the rod feed rate in order that the rate of volume in equals the rate of volume out, and thereby, precluding a build-up of molten glass rod 40 in the furnace 13.

FIGURE 5 represents one type of device used to measure fiber diameter. The ber 40a is journaled between rollers 19 and 20. Roller 19 has a stationary axis, however, roller 20 does not. Roller 20 is attached to arm 21 and is arranged to pivot about point 22. The arm 21 is spring biased in such a manner that the arm 21 conjointly with roller 20 will always bear light pressure against the ber 40a. The arm 21 is mechanically coupled to member 26 and member 26 is biased in thesame direction as `arm 21 by means of spring 25. Member 26 has a mirror 27 attached thereto and serves to reilect any light rays 33 incident thereupon to stationary mirror 3&7. The rays 33 are generated by source 28, which may take the form of a lamp, and passes through horizontal slit 29 and impinges the mirror 27. After a number of reflections the light passes through a triangular (or any other geometricshape) aperture 31 and is incident upon transducer 32. In this particular embodiment, transducer 32 is a photoelectric cell.' The signal generated by transducer 32 is dependent upon the amount of light incident thereupon. This amount of light 33 (see FIG. 5A) varies as to the relative positions of the image of the slit and the triangular aperture, the triangular aperture 31 having its base parallel to horizontal slit 29 and is arranged such that a greater amount of light is passed by aperture 31 if the light ray 31 is incident at the base of triangular aperture 31.

In operation, any variation in liber diameter is transmitted about pivot point 22 by the conjoint action of roller 20 and arm 21. Any action thereby, displaces mirror 27 about its vertical axis around its pivot point 23. Consequently, the angle of incidence of the light 33 upon mirror 27 is changed by an amount linearly proportional to the angular deviation of mirror 27 from its vertical axis. Such deviation vertically displaces the point at which beam 33 passes through triangular aperture 31. In this way, any variation in the diameter of fiber 40 changes the amount of light passing through aperture 31. Hence, a change in fiber diameter is converted into a mechanical variation and ultimately as an electric signal from transducer 32.

The optical amplification of fiber diameter variation I is best understood by referring to FIGURE 6. The coordinate y represents the vertical axis of mirror 27. And the ordinate x represents the horizontal. When a change in fiber diameter occurs mirror 27 is angularly displaced about its vertical axis y by an angle represented by the dotted line y. Prior to such deflection light beam 33 was incident upon mirror 27 at an angle 0. After deection, the angle of incidence remains unchanged when measured from the ordinate x. However, since the angle of retiection equals'the angle of incidence; when measured from x it is 0+qb. Then, if the angle of reection iS measured from the ordinate x it is 1H-2o. Where 2p represents twice the angular deviation lof mirror 27. Since mirror 27 was deflected in proportion to the variation in ber diameter, it thus can be seen that for every reection from mirror 27 the magnitude of angular deviation is doubled.

With the optical measuring system depicted in FIGURE 5 we have obtained accuracy of measurement, which. was measured to be plus or minus one micron in fifty microns. In use, the unit appears to have very little affect on the drawing of the liber 40a and seems to provide a stabilizing inue'nce. However, due tothe extremely high 4sensitivity of the device, the signal derived from the passage of fiber 40a through it contains periodic uctuations caused by the lack of concentricity in rotating parts and similar mechanical reasons.

In general these fluctuations are of a high frequency compared to those it is required to measure and in this embodiment a simple resistor-capacitor filter circuit serves to separate the required components. -v

FIGURE 7 depicts another type of ber diameter meas# uring means 18 that is more stable than the optical sys-y tem and furthermore, provides an A.C. signalcutput which isimore useful to control the velocity of the various servo-motors. This system comprises the sarnerollers 19 and 20 operating on the same principle as that described in connection with FIGURE 4. However` the angular displacement of arm 21 is converted intoa horizontal deviation and operates as follows. The arm 21 is secured to a slug 37 which forms a part of transducer core 36. A sixty cycle magnetomotive force is applied to the transducer, on leads 38, forming part of a magnetic circuit on the center leg of core 36. The outer legs of core 36 complete the magnetic circuit and have coil 39 wound therearound. Coil 39 represents the output circuit and detects any changes in ux in the outer legs of core 36. By varying the position of slug 37 .the flux distribution in the outer legs of 36 is changed. Since coil 39 is responsive to flux change, it detects the'variation in flux distribution and represents it by a change in amplitude of the A.C. signal. This output signal is coupled to a differential ampliter and used in the man1'. er previously described.

` Applicants description has shown the ber 40a to be coated prior to liber measurement, however, it is noted that the order of fiber measurement andcoating is interchangeable and for best results tiber measurement should occur prior to ber coating. This arrangement is best in thatl the possibility of coating material 14e building up on rollers 19 and 20 is eliminated thereby. l

After the ber 40a passes through liber measurement means 18 it is reeled on take-up drum 49. Take-updrum 49 is driven by variable take-up motor means 51 responsive to control signal 47 from master comparator 44.

As shown in the drawings and particularly in FIGURES 2 and 8 the take-up mechanism is arranged to wind the fiber 40a in a helical fashion. Take-up drum 49 is driven by velocity controlled servo-motor 53 responsive to master comparator 44 in the form of a compensated control signal fed thereto. Drum 49 starting mechanism 55 and motor 53 are all secured to carriage 59. Carriage 59 has a passage extending therethrough and is threadably engaged to shaft 58. Shaft 58 is operably connected to traverse servo-motor 54. Motor 54 rotates shaft 58 via gear box 54a. Gear box 54a includes a magnetic clutch reversing assembly responsive to adjustable stop switches 56 and 57. Each clutch in the reversing assembly is constantly in mesh with the drive from the motor by means of a bevel gear. When carriage 59 reaches its limit of travel in either direction a switch is tripped at stop 56 or 57 and switches the operation of motor 54 from one clutch to the other in gear box 54a. In this mode, reversal of traverse is accomplished. Furthermore, this method isolates the backlash within the motor v 54 and gear box 54a from the motion reversal of the carriage 59.

After the speed of the take-up drum has reached the proper rate for the required fiber diameter the fiber is4 passed between drum 49 and starter 5S including pulley 55a. The fiber 40a is stuck to the drum by means of an adhesive tape affixed to the edge of drum 49. Starter 5S, by means of pulley 55a, urges fiber 40a against the adhesive layer on drum 49 thus creating adhesion therebetween. The moment after fiber 40a passes between starter 5S and drum 49, starter 55 is withdrawn by means of a solenoid allowing the drum 49a to reel the attenuated bers. The electrical connections necessary for the operation of the apparatus shown have been omitted from the drawings only in the interests of simplicity of illustration and not as a result of oversight or lack of' technical comprehension.

In operation, the proper furnace temperatures arr selected and preset by means of pyrometers 35. The glass rod is suspended above the furnace 13 and guided by capstans 11a-c. Capstans lla-c are laterally adjustable by means of knob 11d (see PIG. l) to compensate for various glass rod 40 diameters.

The required fiber diameter is set on the calibrated control 42. Control 42 thereby generates a signal proportional to the desired fiber diameter into master cornparator 44. The signals from comparator 44 are taken off voltage divider networks included therein and coupled to their respective subservo-systems. The control signals coupled to rod feed means 11, coating feed means 16, and traverse unit 52 come from taps off voltage dividers referenced to ground. These voltage dividers are ineluded in master comparator 44 and serve to couple any error signal generated to the proper circuits and in the proper magnitude. However. the control signal fed into tibet winding means 51 is taken off a resistor, included in comparator 44, with a floating potential reference. If this were not done a changing signal would result in equal percentage change of all the controls and hence, effectively no change at all. The couplers from the comparator 44 need not be potentiometers but may be transformer couplers for example, variacs.

After the proper rates have been established a drawn fiber 40a is passed through coating boat 14 liber diameter measurement means 18 and onto pick-up drum 49 as hereinbefore described. From this point on the machine will operate by itself in the following manner: the fiber diameter is continuously monitored and a signal proportional thereto is continuously compared to the desired signal corresponding to the desired fiber diameter in differential amplifier 41. lf there is any difference in magnitude therebetween an error signal is generated which is fed to master comparator 44. Stich error signal is compared to the desired fiber diameter signal and causes a compensated control signal to be generated and fed to the various servo-motor systems previously described. The light 70 (see FlG. 1) serves as a heat source and is selected to generate enough heat to render the coating 14C adhesive. Hence, as the fiber 40a is rceled on drum 49 the adhesive state of the coating 14e fuses the wound fiber together. However, if the fibers 40a are not to be fused one need only turn off the light 70. ln this way, fused optical fibers with uniformity independent of furnace temperature via the measurement of one variable are automatically manufactured.

In one application of the embodiment described, elements 13a and b of furnace 13 were controlled by one pyrometer 35a to maintain a constant temperature of l640 F. Elements c and d in furnace 13 were connected through selector 34 to the other pyrometer 5b and adjusted to maintain a constant temperature of 1400 F. The rate of rod 40 fed into furnace 13 was preset to H0 inch per minute. Take-up drum winding rate was 400 r.p.m. The drum 49 was five inches in diameter which corresponds to a linear velocity 6280 inches per minute. The traverse rate was calculated and set to be V: inch per minute in a direction lateral to the direction of winding of fiber 40a. Under these conditions uniformly fine fibers having a diameter in crossection of 75 microns were produced.

Turning now to the preferred embodiment of our invention, the readers attention is directed to FIGURE 9. This embodiment is preferred in that once the machine is set into operation only two rates are varied and furthermore, the machine is equipped to turn off automatically if there is a break in fiber 40a. The components and elements involved in this embodiment are essentially the same as those previously described except as distinguished above.

Included in the fiber diameter measurement means is a high pass filter in parallel with the low pass filter and a meter M1 in series or parallel with the output of the low pass filter. As was discussed, the low pass filter only passes the low frequency signal corresponding to the fiber diameter. Such signal is fed into meter Ml which may take the form of an ammeter or voltmeter whose scale is calibrated to read directly in microns. The high pass filter only passes that signal due to vibration and noise of the machine. The high frequency signal is fed into a detector in the power supply control which operates a solenoid acting as a power supply switch. Hence, if the fiber 40a breaks` the measuring device will no longer vibrate, in that there is no longer a fiber 40a passing therethrough, therefore, the high frequency signal ceases to be generated and the detector sensing the absence thereof is arranged to open the solenoid and thereby cut off the power supplied to the machine.

The glass rod feed, and coating feed are preset according to predetermined values for a calculated fiber diameter in their respective units N3 and N4. Once these controls are set they do not depend upon fiber diameter measuring means 18 for further correction as in the previous embodiment. The take-up drum winding rate is preset, in unit N1 by means of the potentiometer coupled to the input of the servoamplier. Traverse rate is also adjusted prior to operation of the machine by a potentiometer in unit N2.

Included in diameter measuring means 18 is a selection control with a dial calibrated to read directly in microns. This control is mechanically connected to roller 20 and is to vary its displacement from roller 19. The functions of the selector is to adjust a spacing between pulleys 19 and 20 corresponding to a desired fiber diameter and to cause zero error signal to be generated (substantially low frequency signal) at this spacing. In other words, if a fiber 40a varies the spacing between rollers 19 and 20, from its adjusted value, an error signal is generated.

FIGURES l0 and 11 depict the traverse and take-up nation 62 journaled between the gears 60. A pyramidally shaped termination 62 will provide adequate support, however, other geometries may be equally suitable. The terminations 62 of posts 69 have bearings 63 embedded therein and are arranged to cooperate with the at planar portion of gears 60, whereby the drums are free to rotate conjointly about their horizontally fixed axes.

Cooperating with the bevel gears 60 is pinion gear 61 driven by servo-motor l53. Motor 53 provides the winding motion to drums 49. Servo-motor 53 is velocity controlled and is regulated in a manner previously described. In order to provide electrical connection to motor 53 from the amplifier in unit N, (see FIG. 9) shaft66 extends above the upper surface of turntable 65 and has slip rings 71-76 axed thereto. Electrical contact is established by contact members 77--82 which are connected to the amplifier in unit N1.

Turntable drive shaft 66 is cam operated and the cam is designed to provide a constant linear velocity between the edges of the drum (dotted lines 68h). On the other hand, when the wound liber 40a is approaching the edge of a drum 49 (the dotted line) the turntable very rapidly moves a distance' equal to that ybracketed by numeral 68. At this point the cam operating drive shaft 66 has completed its cycle. As turntable 65 very rapidly moves to the next drum 49 liber 40a engages a wedge 64, which is wider than the gap 68 between the drums 49 but less than the width of gap 68a and transports fiber 40a over gap 68 and drops it onto the next succeeding drum 49 at the point indicated by the dotted lines `on the drums. Wedges 64 are stationary relative to the drums 49 and are mounted on turntable 65. l

The liber 40a is prevented from entering the area between the drums 49 by the wedge 64 and the arrangement of the drums 49 in that they are contacting each other at points 67.', and as such drums 49 form a continuous circle vof winding means on turntable 65. Hence, by winding in the direction shown (from the underside of thedrurn) the ber is continuously wound on succeeding drums as they are rotated by turntable 65. By the arrangement described, multiple layers of aligned fibers (in side by side parallel relationship) are mass produced without the use of drum direction reversal means and/ or quickreturn traverse mechanisms. The outer edges of drums 49 may have rubber flanges in order to maintain light pressure contact at points 67 therebetween and thereby minimie-..wear. Furthermore, wedges 64 may be hollow and contain a sponge like area along the face of the wedge engaging the fiber 40a. By lilling wedges 64 with glue, such glue will be applied to fiber 40a as it passes thereover thus insuring adhesion of liber 40a to the next succeeding drum 49.

In operation, the first step is to set `the rates for the drum take-up N1, traverse means N2, rod feed means N3, and coating feed means N4. The overall speed control is, with switch S1 in the open position, varied from a speed near zero r.p'.m. up to the desired drum take-up speed. The signal from the overall speed control is fed, in parallel, -to means N1, N2, N3, and N4 and controls their respective units in accordance with their preset values.

As the overall speed is increased, and fiber 40a is drawing down to its desired diameter, meter M1 will approach a zero error signal reading because means 18 is approaching the point at which the error signal is zero. Now switch S1 is closed and the machine produces aligned coated bers 40a by controlling only the winding and traverse rates. To this end, any error signal generated by means 18 is algebraically added to the overall speed control signal in units N1 and N2. More particularly, the signal from the low pass filter will add or subtract to the magnitude of the overall speed signal regulating units N, and N2 and accordingly, change the control signal fed into variable speed servo-motors 53 and S4. Furthermore, variable speed servo-motors 53 and 54 include Itachotneters that continuously generate rate signals which are compared to the adjusted overall speed signal in their respective amplifiers and any errors therebetween, resulting in compensating control signals coupled respectively to their motors 53 and 54 thereby adjusting their speeds to reduce the errors -to zero. It is noted that the circuitry of traverse unit N2 is not illustrated in FIGURE 9 in that it has the same stages as that depicted for unit N1.

In essence, what is accomplished is tomake all but one of the parameters affecting the diameter of fiber 40a (winding speed, feed rate and temperature) constant, at the desired tiber size, and accurately controlling such size by regulating one parameter; the winding speed of the machine.

It is noted that the dimensional ratio in cross-section of rod and cylinder of the dielectric material supplied to the furnace 13 is fixed for any single operation of the machine in any of the embodiments heretofore described. In other words, the ratio is fixed and dependent upon the particular sizes of dielectric rod and cylinder assembled to form rod 40. In many applications this ratio may want to be changed before the supply of rod 40 is completely consumed. To this end, the furnace illustrated in FIGURE 13 was designed, and is used in conjunction with, or in place of, furnace 13. The furnace depicted in FIGURE 12 enhances the versatility of the machine enabling instantaneous variation of the dimensional ratio in crosseection of rod land cylinder comprising dielectric material 40.

Cylinder 84 and base plate 85, secured together by means of bolt 86, integral with and extending from-cylinder 86, and nuts 87 form the outer vessel of the furnace. This outer vessel is adapted to contain dielectric material 103 which has a specific index of refraction Nd. An inner vessel concentric with said outer one is defined by cylinder 83 having a tapered open ended portion 83a. The inner vessel is adapted to contain dielectricmaterial 104 having an index of refraction Nd which is numerically higher than that of dielectric material 103. The materials `are kept in a plastic state by electric heat means 88.

Use is made of the well known principle that a material in its viscous plastic starte will not ow freely from the reduced opening of a container if the upper end of said container is air-tight. To this end, plungers 90 and 97 are provided in sliding, substantially airtight relation with said inner and outer vessels. That is to say, annu lar disc 97 with shafts 95 `and 96 extending upwardly therefrom is interposed between the inner wall 'of` cylinder 84 and the outer wall of cylinder 83. Likewise, circular plate 90 is interposed between the inner walls of cylinder 83 with shaft 89 extending upwardly-therefrom. In order to extrude dielectric 104 from the outervessel, a vertical force f1 suflicient to extrude the dielectric104 is 'applied thereto. Similarly, force f2 is applied to shafts 9S and 96 and coupled to the medium by disc 97. In this manner dielectrics 103l and 104 are extruded from their respective openings at the bottom of the vessels at auniform rate. f

'In any application of the machine a particular disc .85 with a certain diameter opening is selected andsecured to cylinder 84. By such selection, the extreme .limi-t of coating thickness is established and may be thought of as a coarse adjustment.' In addition, -a fine^'adjust ment is provided by enabling vertical displacement of the inner vessel by utilizing its sloping termination 83a.

FIGURE 13 illustrates the principle iustment mechanism of this furnace. configuration of inner vessel 83a depicts its uppermost vertical extent. In its uppermost position it will readily be noted that the amount of dielectric 103 extruded from its container will be greatest; hence, maximum coating thickness. However, the inner cylinder 83 can be lowered to a point whereby its lower termination 83a touches the in disc 85 arid thereby prevents any flow of dielectric 103. By this expedient, one can establisha maximum coating thickness (coarse adjustment) and by vertically displacing said inner cylinder 83 a fine adiustment within the range selected is obtained.

The fine adjustment is operated by the mechanism secured to base plate 94. Base plate 94 is bolted or welded to the frame 50. Secured -to the inner wall of cylinder 83, and extending upwardly therefrom, arc rods 91. Rods 91 ass through circular openings in ase plate 94 and are secured 'to threaded -annular disc 92. Disc 92 is adapted to cooperate with the inner threaded portion of coupling 93. Coupling 93 is arranged to rotate about its central axis. The outer circumferential portion of coupling has bevel gear 99 machined thereon. Bevel gear 99 cooperates with pinion gear 100 which couples rotational motion thereto. Pinion gear 100 is driven by shaft 101 which in turn is motivated by hand wheel 102.

By rotating hand wheel 102 coupling 93 rotates and dependent upon the direction and the pitch of the threads on coupling 93, the cylinder 83 will be displaced a discrete distance in a vertical direction. Hand wheel 102 has an indicator 103 affixed thereto. The projection of pointer 103 on a calibrated index mounted on wall enables a determination of the opening in the outer vessel. For example, if the slope of the conical portion 83a of the inner vessel were 45 degrees, the vertical displacement of the vessel will change the size X2 of the opening by an equal amount. On the other hand, if the slope of cylinder 83a were not 45; a simple triginometric calculation would readily enable one to determine the size X2 of the coating opening.

From the foregoing it will be seen that we have provided a novel automatic drawing machine capable of producing uniformly small coated optical fibers or aligned fused fiber bundles independent of furnace temperature with a high degree of accuracy.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. For example, the transducer employed in measurement means 18 could talee the form of a capacitance probe forming part of an electronic oscillator. the error signal would be in the form modulated signal and would of the fine ad- The dotted line require a discriminator or ratio detector to transform such signal into a more usable is highly accurate and is many other fields; viz., the phonohigh fidelity audio system. Another possibility would be a collimator type measuring system. That is to say, the shadow of the fiber 40a would be compared to a reference size and would generate an electric signal proportional to any difference therebetween. Also, a different traversing mechanism may be employed, i.e., a guide that would cause the fiber to travel the length of drum 49 and the drum itself would have no translatory motion.

Many other combinations proper fiber alignment. One example, would be a fiber guide with substantially instantaneous travel return whereby very little of the fiber 40a would be non-parallel to the previously wound fiber. Furthermore, the apparatus may be used for drawing conical fiber bundles. To this end, the proper gradient is selected for furnace 13 whereby a conical fiber melting configuration is established. However, inasmuch as fibers are the starting material, it is noted that in this application the fiber diameter measuring means would not be included in the graph transducer in a are possible for enabling operation of the machine. Another obvious modification would be an additional coating of cement to fuse the fibers and thereby eliminate the necessity of heat source 70. The additional coating device should contain an adhesive type material to secure the successive fibers, side by side. For this purpose waterglass, glass solder, or other suitable epoxy resins will give good results.

Accordingly, it is to be understood that within the scope of the appended claims the invention may be practiced otherwise than has been specifically set out in `this specification.

We claim:

l. In combination a system for drawing a thermoplastic material into fine flexible aligned fiber bundles comprising'. a multisection furnace for heating said material; means for selecting various temperatures for the individual sections of the furnace; means for maintaining said temperatures constant; means for feeding the thermoplastic material into the furnace at a predetermined constant rate; means for drawing said material from said furnace into a fine flexible fiber at a constant rate; means for detecting any variation in the diameter of the fiber after it has been drawn from the furnace; means for displacing said drawing means in a direction lateral to the drawing direction so t at the fiber is wound in aligned, multiple, parallel, layers upon said drawing means; and means responsive to said detecting means for regulating the rates of the drawing means and the displacing means in accordance with any detected variation in the diameter of the fiber.

2. 1n combination a system for drawing a thermoplastic material consisting of a dielectric encased by another dielectric having a lower refractive index but substantially the same melting point into fine, flexible, aligned fiber bundles comprising: a multisection furnace rfor heating said material', means for selecting various temperatures for the individual sections of the furnace; means for maintaining constant; means for feeding the thermoplastic material into the furnace at a predetermined constant rate', means for drawing sai material from said furnace into a fine liexible fiber at a constant rate', means any variation in the diameter of the fiber after it has been drawn from the furnace; means an adherent opaque coating to the fiber after it placing said drawing means in a drawing direction so that the fiber is parallel, layers upon said drawing means; and means responsive to said detecting means for regulating the rates of the drawing means and the displacing means in accordance with any detected variation in the diameter of the fiber.

3. ln combination a system for drawing a thermoplastic material consisting of a dielectric encased by another dielectric having a lower refractive index but substantially the same melting point into fine, flexible, aligned fiber bundles comprising: an inner vessel for heating the dielectric material having the lower refractive index; an outer vessel surrounding said inner vessel for heating the other dielectric material; menus for cxtruding both dielectric materials from reduced annular openings at the bottom of their respective vessels such that the extruded dielectrics arc concentric with each other and form :in integral nondiffused solid; a multisection furnace for rcceiving and for selecting various temperatures for the individual sections of the furnace; means for maintaining said temperatures constant; means for feeding said solid into the multisection furnace at a predetermined constant rate; means for drawing said solid from said furnace into a fine flexible fiber at a constant rate; means for detecting any variation in the dinineter of the fiber after it has been drawn from the furnace; means for detecting a discontinuance of drawn fiber from the furnace; means for applying an adherent opaque coating to the fiber after it has been measured;

means for displacing said drawing means in a iirection lateral to the drawing direction so that the ber is wound in multiple, parallel, layers upon said drawing' means; means responsive to said detecting means for regulating the rates of the drawing meansand the displacing means in accordance with any detected variation in the diameter of the fiber; means responsive to the discontinuance detecting means for turning off the system if such a discontinuanceis detected; and means for adjusting the reduced annular opening of said outer vessel.

4. In combination a system for drawing a thermoplastic material consisting of a dielectric encased by another dielectric having a lower refractive index but substantially the same melting point into ne, flexible, aligned fiber bundles comprising: an inner vessel for heating the dielectric material having the lower refractive index, an outer vessel surrounding said inner vessel for heating the otberdielectric material; means for extruding both dielectric materials from reduced annular openings at the bottom of their respective vessels such that the extruded dieiec ries are concentric with each other and form an integral nondifiused solid; means for drawing said solid trom said annuiar openings into a ne exible ber at a constant rate; means for detecting any variation in the diameter of the ber after it has been drawn from the openings; means for detecting a discontinuance of drawn ber from the openings; means for applying an adherent opaque coating to the fiber after it has been measured; turntable means supporting said drawing means for displacing said drawing means in a direction lateral to the drawing direction so that the fiber is wound in multiple, parallel, layers upon said drawing means; means responsive to said detecting means for regulating the rate of the drawing means and the displacing means in accordance with any detected variation in the diameter of the fiber; and means for adjusting the reduced annular opening of said outer vessel.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN COMBINATION A SYSTEM FOR DRAWING A THERMOPLASTIC MATERIAL INTO FINE FLEXIBLE ALIGNED FIBER BUNDLES COMPRISING: A MULTISECTION FURANCE FOR HEATING SAID MATERAIL; MEANS FOR SELECTING VARIOUS TEMPERATURES FOR THE INDIVIDUAL SECTIONS OF THE FURANCE; MEANS FOR MAINTAINING SAID TEMPERATURES CONSTANT; MEANS FOR FEEDING THE THERMOPLASTIC MATERIAL INTO THE FURANCE AT A PREDETERMINED CONSTANT RATE; MEANS FOR DRAWING SAID MATERIAL FROM SAID FURANCE INTO A FINE FLEXIBLE FIBER AT A CONSTANT RATE; MEANS FOR DETECTING ANY VARIATION IN THE DIAMETER OF THE FIBER AFTER IT HAS BEEN DRAWN FROM THE FURNACE; MEANS FOR DISPLACING SAID DRAWING MEANS IN A DIRECTION LATERAL TO THE DRAWING DIRECTION SO THAT THE FIBER IS WOUND IN ALIGNED, MULTIPLE, PARALLEL, LAYERS UPON SAID DRAWING MEANS; AND MEANS RESPONSIVE TO SAID DETECTING MEANS FOR REGULATING THE RATES OF THE DRAWING MEANS AND THE DISPLACING MEANS IN ACCORDANCE WITH ANY DETACTED VARIATION IN THE DIAMETER OF THE FIBER. 